Upgrading RAM is such an easy affair that most of us just do it on our own. Chances are, if you're on a Mac, you're also upgrading your RAM from third-party suppliers. MacIssues points out that if you're adding RAM from someone other than Apple, it's worth holding onto it for a bit.

The reasoning here is pretty simple: Apple's warranty is horrible in regards to RAM:

Apple will only provide warranty service on systems with original Apple-provided RAM in them. Therefore, if your Mac is still under warranty and needs servicing, to get this done by Apple you will have to swap out the new RAM with the old RAM.

Which isn't to say you should go out and pay the egregious prices for Apple's RAM. It just means you should keep those old sticks around as long as your warranty is good for.